The primary objective is to understand the relationship between the structure and function of initiator and non-initiator transfer RNAs. Besides a comprehensive study of the structure, function, evolution and genetic organization of initiator tRNAs, other specific areas of research proposed include: (1) Role of the sequence T psi CG(A) present in virtually all tRNAs in protein synthesis; (2) Role of modified nucleosides in tRNA function -- use of a "tRNA-like" fragment isolated from the 3'-end of plant viral RNA totally lacking in modified nucleosides in such studies; (3) tRNA modifying enzymes and their use as a probe for the secondary and tertiary structure of the "tRNA-like" fragment; (4) tRNAs and genetic suppression in yeast; (5) Mitochondrial tRNAs and their genetic organization; and (6) further improvements in methodology for the sequencing of non-radioactive tRNAs and mRNAs available in small amounts. A variety of approaches are proposed including sequence analysis, in vitro functional studies and the cloning of a mitochondrial initiator tRNA gene to obtain the amounts of tRNA necessary for detailed structure and function studies. Attempts will be made to isolate mutant tRNAs using either cloning of tRNA genes modified at specific sites or using RNA ligase to join synthetic ribooligonucleotides carrying the desired specific alteration to large fragments of tRNAs. It is hoped that these studies will provide a clearer understanding of the central role of tRNAs in protein biosynthesis and also lead to an understanding of the mechanism of general and specific recognition of tRNAs by a variety of proteins.